This invention relates to determining the relative concentrations of fluids within subterranean reservoirs by measuring the chromatographic separation of tracers having distinctly different partitioning coefficients in mobile and immobile phases, such as water and oil phases, of fluids within the reservoirs. More particularly, the present invention relates to improving a process for making such determinations by injecting an aqueous solution of reactants arranged to form CO.sub.2 which is significantly partitioned between such mobile and immobile phases while maintaining an unchanging concentration of acid anions dissolved in the mobile phase.
A method for determining the relative amounts of mobile and immobile fluid phases within a subterranean reservoir by injecting carrier fluid containing a reactant capable of forming within the formation at least two tracers which have different partitioning coefficients between the carrier fluid and the immobile fluid phase, as exemplified by the tracers formed by a hydrolyzable organic ester, and measuring the separation of the tracers, was described in 1969 in U.S. Pat. No. 3,623,842. U.S. Pat. No. 3,751,226 by R. J. Hesse and R. F. Farmer relates to improving such a process by injecting a solution in which the tracer forming reactant is a hydrolyzable beta-keto ester such as ethylacetolacetate. U.S. Pat. No. 3,847,548 relates to improving such a process by injecting carrier fluid containing tracers which partition differently in respect to temperature changes and injecting that fluid a temperature different from the reservoir temperature. U.S. Pat. No. 3,856,468 relates to improving such a process by injecting carrier fluid containing both a precursor which forms a tracer material that partitions between the fluid phases and a tracer material which is inert and substantially completely dissolved in the mobile phase. U.S. Pat. No. 3,990,298 relates to improving such a process by injecting a carrier fluid containing a plurality of precursors each of which forms a tracer which has a distinctive partition coefficient with at least one mobile fluid phase within the reservoir. U.S. Pat. Nos. 4,099,565 and 4,168,746 relate to uses of such a fluid saturation determining process for evaluating the effectiveness of a design process for recovering oil.
U.S. Pat. No. 4,122,896 by R. F. Scheuermann, E. A. Richardson and C. C. Templeton relates to acidizing a reservoir by injecting an aqueous solution of halocarboxylic acid salt so that the rate of the acidization is limited to the rate of it hydrolysis. The disclosures relating to the hydrolysis of halocarboxylic acids contained in that patent are incorporated herein by reference.